That's the thing - There's nothing at all exceptional about that sound. It's a simply arranged and simply (and notice - very quietly and consistently) played part that just fits well with everything else. There's no slappy-poppies, there's no Ricky growl, no flash, almost no dynamics, no nothing. Just solid stuff by a solid player sitting inside a solid mix.
If you could solo it, you'd probably be wondering why it's so boring.
Not hearing a mute (the better players didn't need them anyway), very little compression if any (the decay on the sustained notes sounds freakishly natural). Might be direct, might be an amp - Seemed easier to get that "plain" sound from an amp. Too much "direct" (?) sound going direct. That's not to say it can't be done or anything... With SL on the "probably flatwound" part (again, I think everyone back then used flatwounds unless they were slappers). Less slide noise, more mass, better wear, more sustain with a very light touch. Just a lot of 'neck' pickup with the tone knob turned down.